EUROSOIL 2012. Bari, Italy

Conclusions

Little differences in some soil properties can control the occurrence and persistence of soil WR developed by burning. Previous studies pointed out that texture is one of the main factors, sandy soils being more prone due to the lower

specific surface area (Doerr et al., 2000). Recent investigations also showed that the mineralogy of clay fraction can greatly control the WR in burned soils (Mataix-Solera et al., 2008, 2012). The results of this study confirm previous

research but also include the quality of the initial soil organic matter (depending on the plant specie) as a key factor affecting this property when soil is affected by burning.

The high spatial variability of soil WR in burned areas has been mainly attributed to the expected differences in temperature reached in burned soils as a consequence of the fuel distribution and fire behaviour. But, how little differences in

some soil properties affects to the changes in WR when it is affected by a fire can also help to explain the high spatial variability found under field conditions in burned areas.

References

Arcenegui, A., Mataix-Solera, J., Guerrero, C., Zornoza, R., Mayoral, A.M., Morales, J., 2007. Factors controlling the water repellency induced by fire in calcareous Mediterranean forest soils. European Journal of Soil Science 58, 1254-1259.

DeBano, L. F. 1991. The effects of fire on soil properties. US Department of Agriculture Forest Service General Technical Report, INT-280, 151-156.

Doerr, S. H, Shakesby R. A. & Walsh, R. P. D. 2000. Soil water repellency: its causes, characteristics and hydro-geomorphological significance. Earth Science Reviews, 51, 33-65.

Mataix-Solera, J., Arcenegui, V., Guerrero, C., Jordán, M.M., Dlapa, P., Tessler, N., Wittenberg, L., 2008b. Can terra rossa become water repellent by burning? A laboratory approach. Geoderma 147, 178-184.

Mataix-Solera, J., Arcenegui, V., Tessler, N., Zornoza, R., Wittenberg, L., Martínez, C., Caselles, P., Pérez-Bejarano, A., Malkinson, D., Jordán, M. 2012. Soil properties as key factors controlling water repellency in fire-affected areas: evidences from burned sites in Spain and Israel. Catena (in press)

J. Mataix-Solera1,2, V. Arcenegui1,2, L.M. Zavala2, A. Pérez-Bejarano1,2, A. Jordán2, A. Morugán-Coronado1, G. Bárcenas-Moreno2, P. Jiménez-Pinilla1,2, E. Lozano1,2, A.J.P. Granged1

Key soil properties controlling occurrence and persistence of water repellency after burning

Introduction

Fire induced soil water repellency (WR) is controlled by many different factors (temperatures reached; DeBano (1991), amount and type of fuel, etc., Arcenegui et al. 2007). Some soil properties may determine the occurrence and

intensity of this property in burned soils (Mataix-Solera et al., 2008, 2012). In this research, experimental laboratory burnings have been carried out using soil samples from different sites and collected from under different plant species.

Samples collected at different sites differ in some soil properties, while soil samples taken from the same site vary only in quantity and quality of soil organic matter (SOM), as they were collected under different plant species. The

hypothesis is that the same heating treatment will produce a very different response of WR. The objectives are to advance in the study of soil properties as key factors controlling WR behaviour by heating as to date some questions

remain.

Soil samples, experimental design and methods

Three sites were selected for this study (1 in Cadiz S Spain and 2 in Alicante Province SE Spain) comprising 4 different lithologies (Table 1). Soil samples under different plant species were collected in every site, including: Pinushalepensis, P. pinaster, Quercus coccifera, Q. suber, Rosmarinus officinalis, Juniperus oxycedrus, Erica australis, Pistacia lentiscus and Olea europaea (Table 1). A total of 12 different soil samples from the combination of factors presentwere collected for laboratory heating experiments, and called HF1 to HF12 (Tables 1, 2).

1 GEA - Grupo de Edafología Ambiental Departamento de Agroquímica y Medio Ambiente. Universidad Miguel Hernández. Avda. de la Universidad s/n. 03202, Elche, Alicante, España. Tel.: +34-966658334, Fax: +34-966658340 jorge.mataix@umh.es2 MED_Soil Research Group. Departamento de Cristalografía, Mineralogía y Química Agrícola, Facultad de Química. Universidad de Sevilla, C/Profesor García González, 1, 41012, Sevilla, Spain

Table 1. Main characteristics of the study sites

MED_SoilResearch Group

Soil sample

Sand (%) Silt (%) Clay (%) CO32-

(%) SOM (%) pH EC (µS cm-1)

HF1 80 14 6 2.8 9.5 6.8 127

HF4 62 18 20 3.2 10.4 6.3 54 HF5 72 18 10 0.4 11.1 6.2 76

HF2 32 22 46 0.2 15.5 7.2 267

HF3 34 22 44 0.4 14.5 7.0 268

HF6 22 70 8 21.9 13.0 7.8 394

HF7 42 44 14 33.8 12.8 8.0 323

HF8 36 56 8 21.3 13.7 8.0 306

HF9 36 46 18 31.0 10.9 8.1 274

HF10 54 32 14 60.8 11.8 8.2 380

HF11 46 40 14 69.5 10.4 8.1 357

HF12 58 34 8 68.1 10.0 8.1 402

Table 2. Main characteristics of soil samples

For example, samples HF1 and HF4 come from the same place, with the same lithology and soil type but were taken fromunder different plant species (Table 1). The same situation applies to samples HF6, 7, 8 and 9. Differences in some soilproperties can be observed between them (Table2). In other cases some soil samples come from the same place but aredifferent in lithology and therefore in soil type, soil properties and plant specie, e.g: HF1 and HF2.

Location Coordinates Altitude (m.a.s.l.)

Slope (%)

Pm (mm) Lithology Soil type Soil sample Vegetation

“Los Alcornocales

Natural Park”, Cádiz

36º29’44’’N; 5º38’53’’W 483 6.5 1440

Miocene sandstone Lithic Xerorthent

HF1 Erica australis

36º27’27’’N; 5º37’49’’W 294 13.7 1440 HF4 Pinus pinaster

36º30’53’’N; 5º38’29’’W 538 14.4 1440 Typic Haploxeroll HF5 Quercus suber

36º28’23’’N; 5º37’13’’W 397 5.6 1440 Miocene clay and sandstone

Typic Haploxeralf

HF2 Pistacia lentiscus

36º28’23’’N; 5º37’13’’W 398 8.5 1440 HF3 Olea europaea

“Sierra de la Taja”, Pinoso,

Alicante

38º22’59’’N; 0º58’52’’W 803 3.5 260 Jurassic limestone Lithic Xerorthent

HF6 Pinus halepensis

HF7 Quercus coccifera

HF8 Juniperus oxycedrus HF9 Rosmarinus officinalis

“Sierra de la Grana”, La

Torre de les Maçanes, Alicante

38º35’54’’N; 0º23’33’’W 951 2.2 405 Tertiary limestone Typic Xerorthent

HF10 Quercus coccifera

HF11 Juniperus oxycedrus

HF12 Pinus halepensis

Heating experiments: all soil samples were heated during 20 min in a pre-heated muffle furnace at 200,250, 300 and 350ºC. After cooling, soil samples were kept during a week in an atmosphere chamberwhere air moisture and temperature are controlled: 20ºC and 50% air humidity. WR was measured in allsoil samples using the WDPT (Water Drop Penetration Time) test.

Soil sample

WDPT (s)

Control 200ºC 250ºC 300ºC 350ºC

HF1 2 10383 6120 4 2

HF4 8 7443 1 1 1 HF5 15 9532 972 1 1

HF2 1 7 248 1 1

HF3 3 12 3 1 1

HF6 5 7 1 2 1

HF7 2 3 1 1 1

HF8 2 3 2 1 1

HF9 1 1 1 1 1

HF10 2 2 1822 1 1

HF11 2 3 9 1 1

HF12 2 8 5777 2321 1

HF1

HF4

HF5

HF2

HF3

HF6HF7

HF8

HF9

HF10

HF11HF12

8

9

10

11

12

13

14

15

16

15 25 35 45 55 65 75 85

SoilOrganicM

aer(%

)

Sand(%)

Table 3. Soil water repellency (WDPT s) in the control and heated samples at different temperatures

Results and discussion

Results of WR after the heating treatments are shown in Table 3. Before heating most samples are wettable and only HF4 and HF5 were slightly water repellent (8 and 15 s respectively). The response to the heating treatments wasdifferent depending on the soil sample, with some of them reaching extremely severe WR at 200-300ºC (HF1, HF4, HF5 and HF12), and to the contrary some of them had no WR development at any of the temperatures heated (HF7,HF8 and HF9).

The contrast in behaviour of WR can be explained with the analysis of soil properties of the samples used in this study (Table 2). Results showed that both high and slightly calcareous soils can develop extreme WR. The main soilproperty that affects to the WR response to heating is the texture (Doerr et al., 2000) and especially the sand content, as can be observed in the figure 1. Samples with highest sand content were the ones that developed extreme valuesof WR. It is not the soil organic matter (SOM) content -as we could initially expect- that is the main factor, although between samples with a similar texture it does seem also to have an effect. But we can also observe that samples fromthe same place, and therefore with similar soil properties can respond in a different way due to the plant species factor, thus the quality of their SOM. Is important for example in the case of HF2 and HF3 where the only differencebetween them is that HF2 was taken beneath Pistacia lentiscus and HF3 beneath Olea europaea. In a similar way, comparing the results of samples HF10, HF11 and HF12 that were taken from same place, we can see a differentresponse of WR to heating and it is suspected this is due not only to the slight differences in texture, but also because the quality of SOM, being the formed beneath P. halepensis is more prone to be transformed tohydrophobic whenheated at 250-300ºC than SOM from other species.

Figure 1. Sand (%) vs Soil organic matter content (%) of the different samples. Different colours indicate different maximum persistence classes of WDPT reached after heating. See legend of table 3